_Biology of the Keffir Grain._—The first communication on the biology of the keffir grain seems to have been made by Kern.[51] He regarded the grain as a zoöglœa composed of bacilli and yeasts, the latter being regarded as the ordinary beer yeast (_Saccharomyces cerevisseæ_), while to the former he gave the name of _Dispora caucasica_. As the name indicates, this bacillus possesses two polar spores, and germination of these proceeded in the same manner as with _Bac. subtilis_. As, however, pure cultures of the organisms were not made, and the descriptions and illustrations made by Kern fail to show any distinctive characteristics, it seems probable that accidental confusion with other organisms must have occurred. [Illustration: A MILK FILLING APPARATUS FIG. 10—Where soured milk is handled on the large scale, a special filling apparatus for bottles is desirable, and the soured milk supply should be under cover as shown. This apparatus is made by the Dairy Machinery and Construction Company.] Krannhals[52] succeeded in isolating ten different keffir bacteria among which were several sporulating bacteria. Here too it is impossible to attach any importance to the results, as the artificial preparation of keffir, by means of these bacteria, was not attempted. Beijerinck[53] studied the organisms constituting keffir grains and attached prime importance to the occurrence of two organisms, viz., (_a_) a yeast, _Saccharomyces kefir_, which was capable of inverting milk sugar by means of an enzyme (lactase) and afterwards fermented the products with the formation of alcohol and carbon dioxide, and also (_b_) a non-motile non-sporulating bacterium, afterwards _Lactobac. caucasicus_. The latter, when cultivated on gelatine, gave rise to tough warty colonies about 1/40 in. diameter, and was regarded as one of the lactic acid bacteria found in milk which has been incubated at 77° to 90° F. and afterwards incubated at a higher temperature, 100° to 104° F. Scholl[54] isolated three different organisms, of which a yeast inverted milk sugar for the lactic acid bacteria, while _Dispora_ peptonised the albuminoid matters. Adametz[55] failed to isolate _Dispora_, and came to the conclusion that ordinary lactic bacteria and yeasts played the most important part in the fermentation. Essaulow found in keffir grains six different organisms—yeast cells, cocci, short thick bacilli, bent bacilli, long threads, and motile bacteria. The two latter would seem to be _Bacillus subtilis_, while the others may be regarded as _Bacterium acidi lactici_ (Hueppe), _Bacterium aërogenes_, and _Streptococcus lacticus_ (Grotenfeldt). Pure cultures were insufficient to produce keffir, while mixed cultures of _Bacterium acidi lactici_ and yeasts were effective.